1. Field
The present disclosure generally relates to methods and equipment for fabricating composite resin parts, and deals more particularly with a bladder system used in curing composite parts within an autoclave.
2. Background
Composite resin parts may be cured within an autoclave that applies heat and pressure to the part during a cure cycle. Some part geometries include internal cavities that may cause the part to collapse under autoclave pressure unless a tool such as an inflatable bladder is placed in the cavity to react the autoclave pressure force applied to the part. For example, in the aircraft industry, inflatable bladders may be inserted into the cavities of composite stringer layups that are autoclave cured on mandrel-like cure tools. These bladders are pressurized by venting them to the autoclave pressure.
There are several problems with the vented bladders described above that may lead to inconsistencies in the cured parts. For example, failure to properly vent the bladder may prevent the bladder from becoming pressurized sufficiently to react the applied autoclave pressures. Similarly, insufficient bladder pressurization may result from the failure of sealant tape used to seal a vent hole coupling the bladder with an outside vent. It is also possible for a bladder wall to fail or be penetrated, in which event autoclave gases may be forced into the part throughout the cure cycle. These issues may be particularly problematic where a relatively large number of stringers are cocured at the same time with other parts. For example, where a number of stringers are cocured with a fuselage skin, each of the bladders placed in the stringers is a potential source of leakage into the cocured structure that may cause the entire structure to be scrapped or extensively reworked.
Accordingly, there is a need for a non-vented bladder system that may reduce or eliminate the adverse effects resulting from leaks in the bladder or failure to properly pressurize the bladder. There is also a need for a bladder system and curing method that does not require venting to autoclave pressure, and which may eliminate the need for bladder vent hole seals.